Discussion in '2-Stroke Engines' started by BikeProblems, Apr 20, 2011.

  1. BikeProblems

    BikeProblems New Member

    Hi there,
    I recently purchased a 66cc engine and mounted it to a bike. A couple of days ago, the engine started to backfire when i was reaching close to full throttle. It also felt like it was loosing power. i took a closer look and i think the fuel is com busting in the carburetor.
    Does anyone know how to solve this problem.


  2. DuctTapedGoat

    DuctTapedGoat Member

    Clogged exhaust, too lean a fuel mix? I dunno, got any pics supporting why you think it's combusting in the intake manifold?

    I would guess that you need to adjust your throttle - you're just putting too much gas through the engine, causing it to bog down, and the backfiring is from unburnt fuel in your exhaust igniting.

    Adjust the slide needle, adjust the idle screw, and adjust the throttle cable tension - all to decrease the amount of fuel flow, don't set it to increase or your problems will get worse/more common.
  3. BikeProblems

    BikeProblems New Member

    I think it is combusting in the carburetor because it goes bang and then there is smoke from the carbi all the way down through the inlet manifold to the cylinder.
    Also does lean mean that it is running with to much oil, or not enough.

    Thanks for the advice though, will try
    Last edited: Apr 20, 2011
  4. DuctTapedGoat

    DuctTapedGoat Member

    I honestly don't think you're backfiring out the carb, or else there'd be a melted air filter and flame coming out of your air filter housing. Unless you provide proof that your carb is igniting, I'm running on the assumption that you're just giving it too much fuel. How do you know that your intake manifold is smoking? Do you actually fire it up, wait for it to backfire and immediately take off the carb before the smoke dissipates? I find that /highly/ unlikely.

    Lean means a low amount of oil. Rich means a high amount of oil.
  5. BikeProblems

    BikeProblems New Member

    Sorry about that,
    From what you are describing i too don't think i am backfiring but i am still not to sure what the problem is. Also how would i limit the amount of fuel going into the engine. I have tried adjusting the throttle as well as idle and throttle cable but problem is still there.

    Last edited: Apr 21, 2011
  6. GearNut

    GearNut Active Member

    Lean means the air to fuel ratio has too much air.
    Rich means the air to fuel ratio has too much fuel.
    Both conditions are tuneable by adjusting the slide needle clip position, fuel jet, idle mixture screw (If carb is equipped with one. Not to be confused with an idle speed adjusting screw.), and float height. Sometimes an intake leak causes a lean condition that cannot nor should not be remedied by carburetor tuning. An intake leak needs to be sealed before proper carburetor tuning can occur.
    This is a common point of confusion that has been perpetuated for a looooong time.
    Low oil ratio is just that, a low ratio or less oil to fuel.
    A rich oil ratio is just that, a rich ratio or more oil to fuel.
    The confusion comes into play when the words lean, rich and ratio get jumbled about because they both are used when describing fuel systems on 2-stroke engines.
  7. BikeProblems

    BikeProblems New Member

    Thanks for that. I will check for any air leaks in the intake and if there re any i'll seal them up. If not i will have a go at tunning the carburetor a bit to see what happens.
  8. adb140275

    adb140275 Member

    sounds like ignition problems. check ALL CONNECTIONS and the plug
  9. TucsonDIrect

    TucsonDIrect Member

    Faulty Cdi, or ground wire, the spark is going off at the wrong time, this will happen if you press the kill switch and let it go several times, Could be a bad kill switch too
  10. BikeProblems

    BikeProblems New Member

    I have checked the leads as well as the plug. Although i still have the same Chinese plug that comes with the bike, could this play a problem. The ground wire is straight on metal so it should not be that. Don't think it is the kill switch.
  11. TucsonDIrect

    TucsonDIrect Member

    Just Because its straight on metal does not mean its good ground, where is it "straight on" metal? remember that these kits use a ChinaLume That isnt quite known, or consistent

    Remove the kill switch anyways
    Check your plug, or better yet just replace it,

    Let us know the results

    Did you try turning the gas off and runnning it dry to see if it backfires?

    Does it "4 stroke?"
  12. GearNut

    GearNut Active Member

    Yes it could. The stock plug is not known for reliability.
    Try an NGK BP6HS or BP7HS.

    Also, if you are using the factory plug together wire connectors, They are horrible. Cut them off, strip, solder and seal each connection with heat shrink tubing. If you cannot easily get heat shrink tubing at least strip and solder the connections and use electrical tape to insulate and seal them. I cannot recommend electrical tape for extended use and recommend using heat shrink tubing ASAP.
  13. BikeProblems

    BikeProblems New Member

    Were would i be able to buy an after market NGK spark plug. Would they have them at motorbike stores or are they more of a lawn mower/whipper sniper kind of plug.
    Thanks for the help.
  14. DuctTapedGoat

    DuctTapedGoat Member

    Any auto parts shop will have them.
  15. BikeProblems

    BikeProblems New Member

    Thanks guys for all your help,
    I waked a new plug into it (NGK bp6hs) as well as removing the kill switch and running a fresh batch of gas through the bike.

    it is running great, no bogging of power and no more problems. Although the end of my exhaust is lose. It sounds good but is it bad for the bike

    Thanks again.
  16. DuctTapedGoat

    DuctTapedGoat Member

    I'm glad you got it figured out!

    It's not necessarily bad for your bike, but it will hinder performance in the top end. You'll get more immediate acceleration and hill climbing, but you won't top out very well.

    I suggest you tighten your baffle up.